Study On Construction Of Bismuth Oxyhalide-based Photoelectrochemical Sensor And Quantitative Detection Of Water Environmental Organic Pollutants

With the rapid development of industry and economy,the problem of environmental pollution has become a key issue that humanity needs to solve urgently.Among them,the water environment on which mankind depends is being violated by organic pollutants.Organic pollutants often have long-term effects on water environment,and their damage to environment and human health is mostly irreversible.Therefore,developing an efficient and sensitive analysis technology is vital for the detection of organic pollutants in the water environment to minimize the harm to humans.Compared with traditional detection methods,photoelectrochemical(PEC)sensors have the advantages of low background current,high sensitivity,low cost,short time-consuming,simple reaction equipment,etc,and are widely used in the detection of drugs,organic pollutants,metal ions and other substances.However,the detection performance of the PEC sensor depends on the choice of photoactive materials.The ideal photoactive materials should have a low electron-hole recombination rate to obtain stable photocurrent density.Bismuth oxyhalide(BiOX(X=Cl,Br,I)),as a typical semiconductor,has been widely used in the fields of photocatalysis and photoelectrocatalysis,owing to its unique layered structure,chemical stability,non-toxicity and corrosion resistance,etc.Nevertheless,BiOX(X=Cl,Br,I)materials have a low utilization rate of sunlight,and easily recombined photogenerated carriers,resulting in unsatisfactory PEC performance,which limits their application in PEC sensing field.Therefore,designing some appropriate strategies such as bismuth-enrichment strategy,defect engineering,construction of heterojunctions,metal deposition,morphology control,and element doping,to promote PEC performance of BiOX(X=Cl,Br,I),which is crucial for the signal amplification of BiOX(X=Cl,Br,I)-based PEC sensor and their practical value.In this paper,precious metal deposition,non-precious metal surface self-reduction and coupling graphitic carbon nitride(g-CN)to construct heterojunctions strategies to enhance the utilization of BiOX(X=Cl,Br,I)materials to visible light and promote the separation of photogenerated carriers,thereby to obtain excellent PEC performance.In addition,the essential mechanism about the enhanced PEC performance of BiOX(X=Cl,Br,I)materials is also explored.Based on the excellent PEC performance of these BiOX(X=Cl,Br,I)materials,a series of PEC sensors are constructed to detecting environmental organic pollutants.And the"structure-effectiveness"relationship among metal deposition,non-precious metal surface self-reduction,construction of heterostructures,and detection performance of the PEC sensor have been systematically studied.The constructed PEC sensors show outstanding analytical performance in the process of detecting organic pollutants,which broadens the application of BiOX(X=Cl,Br,I)-based PEC sensors in the field of environmental analysis.The specific research content of this paper is as follows:(1)Precious metal Au deposited BiOCl(Au/BiOCl)composites were prepared with a solvothermal method,and was utilized as photoactive materials to construct4-chlorophenol(4-CP)PEC sensor.The unique local plasmon resonance effect of Au not only optimizes the light absorption performance of BiOCl,but also accelerates the generation,transmission and effective separation of carriers,and finally endows Au/BiOCl composites enhanced PEC performance.In view of the SPR effect of Au and the mechanism of photocurrent increase caused by hole oxidation of 4-CP,the established sensor exhibited a linear range of 0.16-20mgL^-1 in response to 4-CP,a detection limit of 0.05mgL^-1,good stability and selectivity.(2)The self-reducing deposited metal on the BiOCl surface has a denser contact interface compared to the conventional metal deposition,which is conducive to the transport of photogenerated carriers.Bi/BiOCl composite was prepared by self-deposition of BiOCl,and a PEC sensor of ciprofloxacin(CIP)was constructed.The introduction of metal Bi can enhance electron transport and promote the separation of electrons and holes,thus,Bi/BiOCl/indium tin oxide(ITO)electrode can exhibit significantly enhanced PEC response capability compared to BiOCl/ITO electrode.The PEC sensor possessed a linear response range of 0.16-9.64?gmL^-1,and the detection limit can reach 0.05?gmL^-1.The sensor showed excellent stability and selectivity,and provided a new method for the detection of CIP residues in water.Besides,this non-precious metal Bi in-situ auto-deposition strategy laid the foundation for the subsequent research work.(3)BiOCl has a limited spectral response range.In order to broaden the spectral response range of BiOX(X=Cl,Br,I)-based PEC sensors,metal Bi incorporation with the BiOBr(Bi/BiOBr)was prepared by a surface self-reduction method,which can endow Bi/BiOBr with SPR effect similar to that of noble metals,therefore,Bi/BiOBr can be used as a photoactive material to construct a PEC sensor for detecting CIP.A local plasmon resonance effect of metallic Bi was verified by ultraviolet visible diffuse reflectance spectrum(DRS)characterization,the effect not only enhances the light absorption capacity of the composites,but also promotes the rapid transfer of electrons from the conduction band(CB)of BiOBr through the metal Bi to ITO electrodes,resulting in an enhanced photocurrent.Based on the significantly enhanced PEC performance of Bi/BiOBr/ITO electrode,the photocurrent of the sensor showed two linear relationships with CIP concentration range of 16-5087ngmL^-1,and its detection limit can reach 5.3ngmL^-1.In addition,the sensor also showed a good selectivity,stability,and excellent accuracy in the detection of actual water samples containing CIP.Compared with Bi/BiOCl,the Bi/BiOBr-based PEC sensor exhibits a lower detection limit during the detection process of CIP.(4)In order to explore the influence of Bi SPR effect on detection performance in visible light-responsive PEC sensors and explore the general applicability of metal Bi autodeposition strategies to improve the performance of BiOX(X=Cl,Br,I)-based PEC sensors,the Bi/BiOI composites were prepared by the ionic liquid-assisted solvothermal method,and the Bi/BiOI composites-based PEC sensor was constructed to detecting phenol(Ph OH).The photocurrent test verified that Bi/BiOI/ITO electrode showed a better photocurrent performance than BiOI/ITO electrode,which can be attributed to the synergistic effect of the local plasmon resonance effect and inherent metallicity of Bi.Because that Ph OH can inhibit the photocurrent of Bi/BiOI/ITO electrode,the photocurrent signal of the PEC sensor decreases linearly with the increase of Ph OH concentration(4-2600ngmL^-1),and its detection limit was 1.3ngmL^-1.In addition,the Bi/BiOI/ITO electrode based PEC sensor showed good stability and selectivity during the determination of Ph OH,as well as an acceptable accuracy in actual sample detection.Finally,by combining the results of Bi/BiOCl,Bi/BiOBr,and Bi/BiOI based PEC sensor,a universal strategy for amplifying the PEC signals of BiOX(X=Cl,Br,I)-based PEC sensors by depositing non-precious metal Bi is proposed.(5)Graphitic phase carbon nitride(g-CN),as a visible light driving material,can match the energy level of BiOBr,which can theoretically enhance the PEC performance of BiOBr.Therefore,the flower-like g-CN/BiOBr composites were successfully prepared by using the semiconductor compound strategy.And a PEC sensor based on g-CN/BiOBr composites was constructed to detecting tetracycline(TC).The g-CN can reduce the recombination of photogenerated electron-hole pairs and increase the visible light utilization efficiency of BiOBr,thereby enhancing the PEC performance of g-CN/BiOBr composites.Under light irradiation,the photocurrent of g-CN/BiOBr/ITO electrode was greatly increased,which was about 6times higher than that of BiOBr/ITO electrode.The sensor was based on the mechanism that the hole oxidizes TC to enhance the photocurrent.In the TC concentration range of 8.0-5200ngmL^-1,the sensor exhibited two linear relationships with a detection limit of 3.8ngmL^-1,as well as excellent selectivity and reproducibility.Besides,this sensor can be used for sensitive detection of TC in actual water samples.(6)In order to shorten the preparation time of BiOX(X=Cl,Br,I)-based materials,and explore the universality of the introduction of g-CN for the signal amplification of BiOX(X=Cl,Br,I)PEC sensors when detecting environmental organic pollutants,this chapter selects the microwave-assisted method to synthesize g-CN/BiOI composite material,and uses this as a photoelectrode to construct a PEC sensor for the detection of bisphenol A(BPA).Compared with the conventional autoclave-assisted synthesis of BiOX(X=Cl,Br,I)materials,the microwave-assisted method only takes 15 min,which reduces energy consumption.The g-CN can improve the light absorption performance of the composites,and facilitate the generation of a large number of carriers.Moreover,the efficiency of carrier transfer and separation is greatly improved thanks to the heterojunction by coupling g-CN and BiOI,endowing g-CN/BiOI/ITO electrode significantly enhanced PEC performance.The photocurrent test found that the addition of BPA can further increase the photocurrent of g-CN/BiOI/ITO electrode.When the constructed g-CN/BiOI/ITO electrode PEC sensor detected BPA,the detection range was 80-3200ngmL^-1,the detection limit can reach 26ngmL^-1,and it showed satisfactory anti-interference ability,excellent stability,as well as acceptable accuracy in real sample monitoring.The successful exploration of g-CN/BiOBr and g-CN/BiOI based PEC sensor revealed that the strategy of coupling g-CN and BiOX(X=Cl,Br,I)to form a heterojunction can effectively enhance the PEC performance of BiOX(X=Cl,Br,I)and amplify the signal of the BiOX(X=Cl,Br,I)-based PEC sensor.These works have broadened the BiOX(X=Cl,Br,I)-based PEC sensors application in the field of environmental detection.